With the onset of more stringent fuel economy and emission standards, internal combustion engines used in today's vehicles are being designed with much tighter operating clearances. These tighter clearances are typically associated with main bearings, connected rod bearings, and valve train components such as hydraulic lifters, lash adjusters, cam phasers, hydraulic tensioners, hydraulic cylinder deactivation solenoids and similarly oiled components. Many of the aforementioned components, such as the hydraulic valve train componentry, run with 5–10 micron clearances during normal engine operation.
The use of these tighter clearances typically results in an engine being much more sensitive to manufacturing and wear debris. Even with an oil filter, it is not uncommon for cylinder head components such as lifters, cam phasers and cylinder deactivation solenoids to become lodged with debris.
The valve train componentry in the cylinder head is typically fed by an internal oiling circuit comprising mating passages in the cylinder block and cylinder heads. A gasket is used to seal the interface between the cylinder heads and cylinder block. The gasket includes openings designed for allowing oil to pass through the gasket as it travels from the cylinder block to the cylinder heads. These openings often include orifices to meter the oil as it passes through the gasket in order to balance the oil pressure between the cylinder block and the cylinder heads. The gasket openings and corresponding orifices serve as the only oil path to the cylinder heads allowing an oil supply that may also include debris to reach, among other things, the cylinder head valve train componentry.
While such conventional gasket and oiling systems work for their intended purpose, today's engines with tighter tolerances in the cylinder head valve train componentry require more stringent control of debris that may be carried by oil in the oiling circuit.